Biophysical properties and cellular toxicity of covalent crosslinked oligomers of α-synuclein formed by photoinduced side-chain tyrosyl radicals

► Photoinduced generation of side-chain tyrosyl radicals of αS produces covalent soluble oligomers. ► Dityrosine crosslinked oligomers of α-synuclein decrease the yield of mature amyloid fibrils. ► Dityrosine crosslinked oligomers of α-synuclein are cytotoxic.